1. Field of the Invention
The present invention relates to methods of sealing and molding with resin an optical device serving as a part of an optical electronic component.
2. Description of the Background Art
Conventionally, for example as disclosed in Japanese Patent Laying-Open No. 61-1067, a 2-piece transfer molding die has been employed to seal an optical device with resin to produce an optical electronic component (or a molded product). The optical device thus sealed with resin is for example a light emitting diode (LED) mounted on a substrate. This LED chip is sealed with transparent resin acting as a lens. Employing such a 2-piece transfer molding die causes a problem depending on the transparent resin's properties, as follows:
The aforementioned transparent resin melts as the die is entirely heated. The melted resin is significantly low in viscosity and accordingly easily leaks out the die's cavity, resulting in resin flash.
Furthermore, the die has a path (e.g., a cull, a runner, a gate, a sprue or the like) to introduce the transparent resin into the cavity. As a result, the resin sealing the optical device and that present in the path would set in one piece.
Furthermore, the set resin at high temperature is small in hardness. As such, the set resin tends to adhere on the cavity's molding surface. As such, if the set resin is in contact with a molding surface having a curved surface corresponding to that configuring a lens, it is difficult to remove the set resin from the cavity's molding surface. Furthermore, if the lens is successfully removed from the die's molding surface, the lens tends to have a surface with protrusion and depression. As such, it is difficult to provide the lens with a mirror finished surface.
Furthermore, if the lens has voids formed therein, the lens unevenly transmits light, resulting in uneven brightness. This impairs the optical electronic component (or product) in quality.
Accordingly, the present inventors have been studying a method employing a transfer less molding die, rather than the aforementioned transfer molding die, i.e., a die free of a resin path and thus reducing unnecessary resin to seal a product with resin. This method employs a mold release film to provide enhanced releasability between the die and the transparent resin and that between the optical electronic component and the die. Furthermore, the die's cavity is defined by a space vacuumed to prevent voids caused while the transparent resin is heated and melted.
Hereinafter the aforementioned method of sealing and thus molding with resin will more specifically be described.
The above described method employs a matrix substrate with a large number of surface mounted optical devices mounted thereon. Furthermore, this method employs a die composed of three pieces (i.e., a top piece, a bottom piece and an intermediate piece) and a mold release film. Furthermore, the die has an internal space vacuumed. This method can solve a problem that has not been overcome by a conventional 2-piece, transfer less molding die, as disclosed in Japanese Patent Laying-Open No. 2004-98364. More specifically, it can prevent the mold release film from wrinkling. This is because the bottom and intermediate pieces can sandwich and thus tension the mold release film.
The 3-piece die disclosed in Japanese Patent Laying-Open No. 2004-98364, however, cannot cover the entire surface of the cavity of the bottom piece with the mold release film. Furthermore, if the cavity's molding surface is a curved surface, the curved surface cannot be appropriately covered with the mold release film. As a result, the optical device cannot be sealed in transparent resin shaped as desired.